Field of the Invention
The invention relates to a control unit for actuating a triggering device for a seat belt pretensioner in a vehicle.
Devices for triggering seat belt pretensioning devices or devices for locking seat belts in vehicles, in addition to devices for triggering airbags, are usually actuated when a front-end or oblique impact occurs, so that, as early as possible after the start of the impact, further forward displacement of the vehicle occupants wearing seat belts is prevented. In this way, the vehicle occupants are effectively protected against injuries caused, in particular, when the head of any of the occupants strikes against a part of the interior of the vehicle or when any of the vehicle occupants dive under the belt.
The article "The new seat belt pretensioning system from Volkswagen" by H. Muller, A. En.beta.len, J. Gunnewig, M. Specht and W. Krauss in the automobile periodical ATZ Automobiltechnischen Zeitschrift, No. 96 (1994), pages 546 to 550, discloses a control unit for actuating a device for triggering a seat belt pretensioner in a vehicle. In this regard, a seat belt device with a safety belt has a control unit arranged directly next to it. Each control unit includes a mechanical sensor device which is constructed as a spring/mass system and is sensitive to vehicle deceleration, and a pyrotechnically operating triggering device. If a sufficiently severe vehicle deceleration caused by a front-end, an offset, a pole or oblique impact is detected, a propellant charge of the triggering device is fired at the earliest possible instant of impact after the impact starts. The seat belt is tightened or tensioned via a cable-actuated coupling.
The published German Patent Document DE 29 34 749 C2 discloses a control unit for actuating a device for locking a seat belt. A sensor device of the control unit senses a vehicle deceleration and, if a sufficiently severe vehicle deceleration is detected, it actuates a contact in a safety circuit of the locking device. In the locking device, the closing of the contact excites an electromagnetic coil and, consequently, moves an armature which effects a mechanical locking of the belt strap of the seat belt.
The published German Patent Document DE 36 21 580 C2 discloses a control unit for actuating a triggering device of a seat belt pretensioning device when a front-end or oblique impact occurs. An acceleration signal which is supplied by a sensor device and which is determined by positive and negative accelerations of the vehicle in the direction of the longitudinal axis thereof is evaluated in an evaluation circuit. The evaluated signal is compared with a threshold value. If the threshold value is exceeded by the evaluated signal, a trigger signal for the triggering device is generated by the evaluation device. The threshold value has the same sign as for the negative vehicle acceleration, so that only a sufficiently negative vehicle acceleration/deceleration, such as is typical for a front-end or lateral impact, can lead to a triggering.